1. Field of the Invention
The present invention relates to a wavelength conversion LED such as a white light emitting diode in which blue light is emitted from a pn junction interface, this blue light is made incident on a fluorescent body to extract yellow light, and white light is emitted by mixing the blue light and yellow light, or alternatively, ultra-violet light is emitted from the pn junction interface and this ultra-violet light is made incident on the fluorescent body to extract intermediate colored light such as white light.
2. Detailed Description of the Prior Art
FIG. 6 shows a white LED as an example of a wavelength conversion LED known in the prior art.
In FIG. 6, a white LED 1 contains a white reflector 2 having a bowl 2a formed so as to open upward, a LED chip 3 disposed close to the center of the bowl 2a of the reflector 2, and an enclosing resin 4 containing wavelength conversion material 4a filled into the bowl 2a. 
The reflector 2 has electrode terminals 2b, 2c which are integrated into a single body by an insert molding or the equivalent.
The LED chip 3 is formed so as to constitute a blue LED chip through the joining of InGaN (p-type) and Sic (n-type), and the pn junction surface 3a which constitutes the light emitting layer thereof is disposed in the expanded area near the upper edge.
In the LED chip 3, the n-side thereof is electrically connected to the electrode terminal 2b exposed at the bottom of the bowl 2a of the reflector 2 while being fixed by, for example, a conductive adhesive; and the electrode 3b on the surface of the p-side thereof is connected by a wire 3c of metal or the like to the other electrode terminal 2c exposed at the bottom of the bowl 2a. 
The enclosing resin 4 comprises a translucent resin and contains fluorescent a body 4a which emit yellow light when exposed to blue light. As the fluorescent the body 4a generally have a larger specific gravity than the enclosing resin 4, as a result of settling, the lower section thereof comprises a dense fluorescent body layer 4b as shown in the figure.
In the white LED 1 configured as described above, when a drive voltage is applied between the n-side and the p-side of the LED chip 3 by the electrode terminals 2b, 2c, blue light L1 is emitted from the junction surface 3a thereof. The blue light L1 emitted from the LED chip 3 is directed towards the opening and bottom of the bowl 2a of the reflector 2 and is approximately uniformly incident thereto.
The blue light L1 directed towards the opening of the bowl 2a of the reflector 2 is emitted upwards as it is.
Meanwhile, the blue light L1 directed towards the bottom of the bowl 2a of the reflector 2 is incident on the fluorescent body layer 4b which has settled at the bottom of the bowl 2a. Accordingly, the fluorescent bodies 4a within the fluorescent body layer 4b absorb the blue light L1, and as a result of excitation, emit yellow light L2 in the form of fluorescent light. This yellow light L2 is mixed with the blue light L1 emitted upwards as it is from the opening as previously described, white light is produced overall; and this is emitted upward.
In contrast, a white LED 5 configured as shown in FIG. 7 is also known in the prior art.
In FIG. 7, the white LED 5 differs in construction with the white LED 1 from FIG. 6 in terms of the vertically-inverted disposition of the LED chip 3; consequently, the pn junction surface 3a of the LED chip 3 is disposed toward the bottom within the fluorescent body layer 4b of fluorescent bodies 4a in the enclosing resin 4.
Similarly, in the white LED 5 configured as described above, a portion of the blue light emitted at the junction surface of the LED chip 3 is absorbed by the fluorescent body 4a as it is passed through the fluorescent body layer 4b, and yellow light is emitted; in addition, the remaining portion of the blue light becomes transparent inside the LED chip 3 through the enclosing resin 4 above the fluorescent body layer 4b, and is emitted upwards from the enclosing resin 4.
As a result of this, the yellow light and blue light as described above are mixed, and white light is emitted upwards.
The following problems have been experienced with configurations characterized by the white LEDs 1, 5 as described above.
In both of the white LEDs 1, 5, a portion of the blue light is emitted upwards as it is from the opening in the bowl 2a of the reflector 2, and in order to obtain white light, yellow light with a light volume which counterbalances the light volume of this excessively-strong blue light is required. Accordingly, the volume of fluorescent bodies 4a which convert blue light to yellow light must be increased. Since the blue light and the yellow light are shielded by the fluorescent body particles, therefore, the volume of light which may be extracted at the opening of the bowl drops, and the overall light emitting efficiency of the white LEDs 1, 5 is reduced.
Furthermore, in the case of the LED chip which emits ultra-violet light, a mixture of fluorescent bodies which emit red, green, and blue light is often used; however, since ultra-violet light is emitted from the top of the chip directly to the opening in the bowl without being incident on the fluorescent bodies in this case also, this light does not contribute to the strength of the visible light extracted from the top, and the light emitting efficiency is reduced.
The similar type of problem occurs in other wavelength conversion LED with same configuration whose fluorescent body composition or the LED chip are modified to emit single colored, infrared, or intermediate colored light.
It is therefore an object of the present invention to provide a wavelength conversion LED which improves light emitting efficiency through the use of a simple configuration.
This object is achieved by the LED of the first embodiment of the present invention comprising electrode terminals, a LED chip, a reflector having a bowl reflecting the light emitted from the LED chip to an opening, a enclosing resin filled into the bowl, and a wavelength conversion material mixed into the enclosing resin, absorbing the light emitted from the LED chip, and emitting light with a longer wavelength than that of the absorbed light, and characterized in that the LED chip is connected to a electrode terminal inside the bowl, and in addition, a conductive reflective member for reflecting the light emitted from the junction surface without transparency thereof on the substantially whole surface is provided at the top surface of the LED chip; the density of the wavelength conversion material mixed into the enclosing resin is larger below the junction surface of the LED chip than thereabove; and/or a wavelength conversion material layer is formed into a prescribed shape on the inside surface of the reflector with the bowl.
In this first embodiment, light is emitted from the junction surface of the LED chip as a result of application of drive voltage from both electrode terminals to the LED chip via the conductive reflective member and is reflected downward by the conductive reflective member.
All or some of the downward directed light is absorbed by the wavelength conversion layer, and wavelength converted light is emitted there.
Accordingly, when the color of the light emitted by the LED chip is blue, the blue light which is not absorbed by the wavelength conversion layer is mixed with the yellow light emitted by the wavelength conversion layer, and is emitted from the top to the exterior as white light. Furthermore, when ultra-violet light is emitted by the LED chip, this ultra-violet light is converted by the wavelength conversion layer and emitted to the exterior as white light. Consideration has been given for diodes which emit non-white light using combinations of wavelength conversion material and LED chip emission wavelength, for example, violet light emission diodes which emit violet light through the combination of a blue LED chip and fluorescent bodies which emit red light, and infrared light emission LED which combines an ultra-violet LED chip with fluorescent bodies emitting infrared light. However, the constitution according to the present invention makes no distinction in terms of wavelength conversion material or LED chip type.
In this case, the light reflected downward by the conductive reflective member is always directed to the high density layer of wavelength conversion material at the bottom of the LED chip, and consequently, the light emitted directly to the exterior from the top of the chip without being converted by the wavelength conversion material is reduced. Therefore, in contrast to the prior art in which a suitable amount of wavelength conversion material must be included in the enclosing resin to fully convert the wavelength of the light emitted upward in order that white light or light of any other intended color may be obtained, the present invention allows the required volume of fluorescent bodies to be reduced. As a result, the light which was shielded from reaching the exterior by particles of the excessive volume of wavelength conversion material is obtainable at the exterior, and the efficiency of extraction is increased for the light emitted to the exterior.
The LED in accordance with the second embodiment of the present invention is characterized in that, in the LED in accordance with the first embodiment of the present invention, the primary side of the junction surface of the LED chip is formed so as to have a larger area than the secondary side thereof, and the side surface of the chip is inclined.
In this second embodiment of the present invention, the light advancing from the side of the junction surface toward a slightly upward direction is reflected downward by the expansion portion expanding in the direction of the primary surface side; consequently, light emitted directly upward from the LED chip can be completely eliminated.
The LED in accordance with the third embodiment of the present invention is further characterized in that, in the LED in accordance with the first embodiment or second embodiment of the present invention, the second conductive reflective member for reflecting the light emitted from the junction surface without transparency thereof on the substantially whole surface is provided at the bottom surface of the LED chip.
In this third embodiment of the present invention, the light emitted downward from the LED chip""s junction surface is reflected upward at the bottom of the LED chip by the second conductive reflective member; consequently, there is no transparency downward from the bottom of the LED chip and no absorption by electrode terminals, conductive adhesives, or the like disposed therebeneath. In accordance, the efficiency of light output and the light emitting efficiency of the LED are improved.
The LED in accordance with the fourth embodiment of the present invention comprises electrode terminals, a nitride semiconductor-type LED chip provided on a conductive substrate, a reflector having a bowl reflecting the light emitted from the LED chip to an opening, a enclosing resin filled into the bowl, and a wavelength conversion material mixed into the enclosing resin, absorbing the light emitted from the LED chip, and emitting visible light; and is characterized in that the LED chip is connected to a electrode terminal inside the bowl, and in addition, a conductive reflective member for reflecting the light emitted from the junction surface without transparency thereof on the substantially whole surface is provided at the top surface of the LED chip; the density of the wavelength conversion material mixed into the enclosing resin is larger below the junction surface of the LED chip than thereabove; and/or a wavelength conversion material layer is formed into a prescribed shape on the inside surface of the reflector with the bowl.
A conductive substrate is used in this fourth embodiment, and for this reason, only one wire is needed to form an electrical connection with the electrode on the conductive reflective layer; consequently, the volume of light which is not available at the exterior as a result of shield by wires is reduced. Furthermore, since the emission of ultra-violet and blue light is carried out using the nitride semiconductor-type LED chip, a wide range of different types of fluorescent body can be combined to efficiently emit visible light with longer wavelengths, and consequently, light with a wide range of colors can be emitted with high levels of intensity.